Fibrillation is a life-threatening medical condition that may be treated with external defibrillation. External defibrillation includes applying defibrillation electrodes to the patient's chest and delivering an electric shock to the patient to depolarize the patient's heart and restore normal sinus rhythm. The chances that a patient's heart can be successfully defibrillated increase significantly if a defibrillation pulse is applied quickly. In many venues, such as airports, health clubs and auditoriums, automated external defibrillators (AEDs) are available to provide life-saving defibrillation therapy. Such AEDs may be used infrequently, in comparison to external defibrillators employed by rescue personnel.
An AED includes defibrillation electrodes, which an operator applies to the chest of the patient and which deliver the defibrillation therapy. The electrodes are typically disposable and are stored within hermetically sealed packages. Sealing electrodes in a package provides protection during shipping, maintains sterility, and prolongs the useful life of the electrodes.
For example, electrode pads include a hydrogel that helps adhere the electrode to the patient, enhances electrical contact between the electrode and the patient, and facilitates administration of a defibrillation shock with a reduced risk of burning the patient. The shelf life of electrode pads is in part a function of the shelf life of the hydrogel. In time, moisture evaporates out of the hydrogel and escapes from the package. As moisture escapes, the safety and effectiveness of the defibrillation electrodes may become compromised. As the hydrogel dries, the defibrillation electrode may become less adhesive, may be less able to detect electrical signals generated by the patient's heart, and may conduct defibrillation shock less efficiently. When the defibrillation electrodes are in a condition in which they are unable to perform appropriately, or are at risk of being unable to perform appropriately, then the defibrillation electrodes are in a condition for replacement.